The present invention relates to an apparatus and process for producing chlorine gas. The present invention more particularly is directed to such a process and apparatus for producing chlorine gas and for employing such chlorine gas for the production of chlorine water.
The apparatus and process of the present invention particularly are capable of discontinuous, intermittent operation and of being fully automated in order to produce small or moderate quantities of chlorine water produced by quantities of chlorine gas of the order of a few grams or even kilograms per work cycle.
Even further, the present invention relates to such an apparatus and process capable of producing chlorine water for small consumers, such as washing machines, dishwashers, disinfecting devices, purifying plants, and the like.
It is known that chlorine water generally is prepared by absorption of chlorine in water. This resultant solution is known to be highly unstable over time, and in practice permits only immediate use without substantial storage or wide spread marketing or transportation.
On the other hand, the production of chlorine gas has been and still is carried out on an industrial scale in large capacity plants, either for direct use, for example for the production of chlorinated solvents, plastic materials, chemical intermediates, etc., or for distribution in tanks or in cylinders. However, for several types of consumers, for example in domestic, hospital, dairy, alimentary and sanitary fields, even this type of distribution, transportation and storage is not practical. As a matter of fact, these types of consumers benefit from time to time from the bleaching, disinfecting and deodorizing capabilities of chlorine. However, the supply of chlorine gas in cylinders for on-site preparation of chlorine water also creates difficulties that are insurmountable in practice. For example, it is necessary to employ skilled personnel to carry out the operation of absorbing chlorine gas into water, as well as due to toxicity problems associated with the handling of chlorine gas. This particularly is true when there is a tendency to eliminate the transportation of chlorine gas in cylinders or in tanks due to the high risks and safety problems connected therewith.
These difficulties become essentially impossible in the case of domestic consumers for whom useful quantities of chlorine gas are very modest and the use of which is variable over a period of time. Accordingly, in these domestic situations, it heretofore has been indispensable to resort to the use of aqueous solutions of sodium hypochlorite, i.e. solutions obtained by absorbing chlorine gas is a diluted aqueous solution of sodium hydroxide, and then diluting this solution to 5% active chlorine. However, in addition to the specific minor active ingredient, such sodium hypochlorite solution provides further problems of being caustic and of emitting irritating and harmful vapors, although these problems of toxicity are relatively minor compared to those associated with the direct use of chlorine gas.
With specific reference to domestic comsumers, proposals have been offered to use in washing machines and dishwashers electrolytic cells for the on-site production of chlorine gas which immediately is absorbed in water, thus forming chlorine water which, during an appropriate stage of the washing cycle, is fed directly to a wash tank. More particularly, there have been proposed electrolytic cells with two compartments, namely an anode compartment and a cathode compartment, the two compartments containing appropriate anode and cathode electrodes, physical separation between the two compartments being achieved by a porous partition or diaphragm which however enables the two compartments to be in electrolytic communication.
In electrolytic cells of this general known construction, during electrolysis of a solution with a sufficient concentration of sodium chloride, chlorine gas is developed at the anode and hydrogen is developed at the cathode, with the release of corresponding quantities of alkali solutions. If the anodic and cathodic products of electrolysis mix with one another, the chlorine and sodium hydroxide react to form a sodium hypochlorite solution, i.e. a hypochlorite cell, thereby cancelling the current yield for the production of chlorine gas. Accordingly, when the primary object of the electrolysis operation is to produce chlorine gas, the products of electrolysis must be prevented from mixing. However, such mixing can occur by two specific means, namely (a) mechanical mixing of the anodic and cathodic solutions, and (b) migration to the anode, under the action of the electric field, of OH.sup.- ions corresponding to the particular alkalinity at the cathode, and the combination of such ions with chlorine gas at the anode. As indicated above however mixing of either type must be prevented when the primary object of the electrolysis operation is the production of chlorine gas.
Another problem of significance with respect to electrolytic cells for the production of chlorine gas intended for the above discussed uses involves the formation of deposits at the electrodes and on the porous partition or diaphragm separating the anode and cathode compartments. As a matter of fact, in order to produce small or even modest quantities of chlorine, it is inconceivable to attempt to carry out preliminary treatments of acidification and purification of the brine, i.e. of the initial sodium chloride solution, to attempt to reduce the concentration of calcium and magnesium salts therein to the order of a few parts per million. Calcium and magnesium salts normally are contained in the sodium chloride and in the water with which the sodium chloride solution is prepared in quantities on the order of hundreds, or even thousands, of parts per million. Such salts precipitate at the cathode, in the cathodic solution, and on the diaphragm or partition as a result of alkalinization which accompanies the generation of hydrogen in the cathode compartment. The precipitation of calcium carbonate and magnesium hydroxide blocks the passage of the electric current and jeopardizes the proper operation of the electrolytic cell, even to the point of irreparably damaging it due to resultant irregular increases in temperature. Particularly, the precipitation of the above mentioned salts effects the porous partition which thus remains at least partially obstructed on the surface thereof facing the cathode compartment, the result being the disadvantages and problems mentioned above.
Attempts have been made to overcome these problems by resorting to an operating cycle whereby the polarities of the electrodes of the cell periodically are reversed, such that each compartment and electrode is operated alternately as an anode and as a cathode. During operation of one of the compartments as an anode compartment, the deposits at both the electrode thereof and on the adjacent surface of the diaphragm are removed and returned to the solution. However, this arrangement, no matter how advantageous it might appear, does not entirely solve the problem.
The possible problem of toxicity of chlorine produced generally can be solved by delivering the chlorine to an in-water absorption tower. However, another problem associated with this type of electrolytic cell results from the mixture of chlorine gas produced in the anode compartment with hydrogen gas generated in the cathode department. Such mixture may become explosive.